1. Field of the Invention
The present invention relates to an imaging lens. In particular, the present invention relates to an imaging lens having a super-wide-angle, four-lens structure that is suitable for forming a image of objects within a wide range on an image-taking surface of a solid image pickup device such as a charge-coupled device (CCD), a complementary metal oxide semiconductor (CMOS), etc. The imaging lens is mounted on an imaging device, such as a camera used to check the rear of an automobile.
2. Description of the Related Art
In recent years, cameras used to check the rear of an automobile are being mounted on automobiles. Images of the rear exterior of the automobile imaged by the camera are displayed on a monitor provided inside of the automobile. As a result, assistance can be provided for driving operations performed when backing up the automobile.
In this type of camera, an image of objects within a wide range is required to be formed on an image-taking surface of a solid image pickup device such as the CCD, the CMOS, etc. Therefore, the imaging lens used in such a camera is required to be a super-wide-angle imaging lens having an angle of view exceeding 130°.
In addition, recently, there has been an increasing demand for such cameras to be smaller and lighter. In accompaniment to this demand, the super-wide-angle imaging lens mounted on such cameras is also required to be small and light.
[Patent Literature 1] Japanese Patent Unexamined Publication 2003-232998
However, conventional super-wide-angle imaging lenses have a large number of lenses and the overall length of the imaging lens is often long. Such imaging lenses are not suitable for achieving reduction in size and weight.
Furthermore, even when the super-wide-angle imaging lens is small, the cost of the imaging lens rises since expensive lenses, such as a gradient index lens, are used. In addition, optical performance deteriorates due to the effect of aberrations, such as distortion.